The etching of hard dielectric thin films on an integrated circuit substrate, such as a boron silicate glass film or a phosphorous silicate glass film, is preferably done using a hard mask rather than a photoresist mask. Such a hard mask, which may be an amorphous carbon layer or ACL, is better able to withstand strong plasma etch chemistries required for efficient etching of a hard dielectric film. A typical device structure consists of a photoresist mask, an anti-reflection coating (ARC) underlying the photoresist mask, the ACL underlying the ARC, and the hard dielectric film underlying the ACL. Each of the layers under the photoresist mask is etched in sequence using different plasma chemistries. Prior efforts to perform each of these etch steps in a single reactor (to maximize productivity) have failed because such attempts resulted in loss of control over critical dimension (feature size) and the occurrence of significant particulate contamination. These problems have not been well-understood, and the industry has avoided them by performing at least some of the sequential etch steps referred to above (e.g., the etching of the ACL in a hydrogen-based plasma chemistry) in a separate dedicated reactor chamber. However, if all the foregoing etch steps could be performed in the same plasma reactor chamber, then productivity would be greatly increased.
We have discovered that one problem with using a hardmask such as an ACL arises from the fluorine-based chemistry that must be used to etch the ARC (typically a silicon oxy-nitride). This chemistry leaves a fluorine-containing residue within the chamber. If the different etch steps are performed in the same reactor chamber, we believe that this fluorine-containing residue subsequently reacts (during the next etch process) with hydrogen present in the hydrogen and nitrogen-based chemistry used to etch the ACL. We feel that the combination of the fluorine and hydrogen reacts with carbon in the ACL to create carbon-containing particulate contamination.
Another problem we have discovered is that the hydrogen present in the nitrogen+hydrogen process gases employed to etch the ACL leaves a hydrogen or hydrogen containing residue in the chamber (on chamber surfaces and possibly on the wafer itself) that remains after conclusion of this etch step. We believe that, during the subsequent etching of the hard dielectric layer, hydrogen from the residue combines with fluorine in the fluorine-containing plasma chemistry used in the hard dielectric layer etch step. This reduces the amount of fluorine available to participate in the etch reaction, slowing down the etch rate and reducing control over the critical dimension (feature size) in the hard dielectric layer. Typically, the critical dimension is reduced below the desired magnitude.
Therefore, there is a need for a process for etching a hard dielectric layer (such as boron- or phosphorus-silicate glass) using a hard mask (such as amorphous carbon) in which the steps for etching the different layers with different plasma chemistries is carried out in the same reactor chamber without loss of control over critical dimension or feature size and without producing particulate contamination.